Lapping method and apparatus



3,305,976 Patented Feb. 28, 1967 United States Patent lilice 3,305,976 LAPIING METHOD AND APPARATUS Wallace W. Koskie, Minneapolis1 Minn., assiguor to Data Products Corporation, St.v Paul., Minn., a corporation of Delaware Filed May 7, 1964, Ser. No.`365,606 8 Claims. (Cl. 51-151) In many diverse pieces of equipment, small mechanical members having surfaces with a very slight curvature (ie. large radius of curvature) are required. It is oftentimes very difficult to form desired surfaces on such members inasmuch as conventional grinding techniques are usually lnot applicable because of the relatively small surface area and the large radius of curvature required. Where machine grinding is not applicable, the surfaces coul-d be formed manually but this would require a 'great deal of time and effort by very skilled persons. Consequently, it is usually extremely costly to provide a large number of such` members each of which has a precisely` curved surface formed thereon. `However, in certain pieces of equipment, the provision of such members is necessary forv the satisfactory operation of the equipment. One such piece of equipment constitutes magnetic disc recording apparatus which often employs magnetic heads of the so-called flying type. In operation, the moving air developed by a rotating disc functions as a bearing to support the ying heads a pre-cise distance away from the disc surface. The heads must each be provided 'with a precisely curved surface in order to establish optimum aerodynamic effects for supporting the heads. In' view of this .and similar applications, it is an object of the present invention to provide an improved method and apparatus for forming slightly and precisely curved surfaces on relatively small mechanical members.

In accordance with one aspect of the invention, curved surfaces are formed on small mechanical membersV by randomly moving lthe member on a lapping plate' having an abrasive lapping compound thereon, which plate is curved to the desired radius of curvature.

In accordance with one embodiment of the invention, the lappingplate forms one surface of a closed container and can be flexed to the desired curvature by controlling the vacuum or pressure within the container. In another embodiment of the invention, the flexible plate is merely supported on a variable amount of flexible padding. In both embodiments, the surface of the mechanical member to be formed is in contact with the plate and a weight is supported on the member to maintain the surface in engagement with the plate. In the second lapping plate embodiment, the weight helps flex the plate to the desired curvature.

In accordance with a still further .aspect of the invention, apparatus is provided for moving the member over the lapping plate in essentially a ligure 8 pattern which pattern simulates random motion.

The novel features that are -considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as Well .as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, -in which:

FIGURE l is a plan view of apparatus constructed in accordance with the invention for moving a mechanical member on a lapping plate in a substantially random-like fashion;

FIGURE 2 is a vertical sectional view of a' preferred embodiment ofthe invention particularly illustrating the manner in which a magnetic head can be supported on a' deformable lapping plate; and f FIGURE 3 is a verticall sectional view of an alternate lapping plate embodiment. 'y

Attention is' now called to FIGURE 1 of the drawings which illustrates a lapping plate apparatus 10 upon which a mechanical member, such as a magnetic head useful in magnetic disc storage systems, can be moved by a transport ring 12 for reshaping or conforming the surface of the mechanical member to the shape or curvature of the lapping plate.

FIGURE 2 illustrates a preferred embodiment of lapping plate apparatus 10 which includes a flexible'lapping plate 14 formed of aluminum or some other material which can be flexed to a desired radius. The lapping plate 14 is supported on a pad 16 formed of a resilient material. The pad 16 is supported on a rigid surface 18. An abrasive compound 20 is spread on the upper surfacev of the lapping plate 14.

The surface 22 of a mechanical member 24, herein shown to be a magnetic head, is supported in engagement with the lapping' plate 14. In order to assure proper engagement of the surface 22 with the lapping plate 14; and in order to deform the lapping plate 14 to the desired curvature, a weight 26 is supported on the head 24. The head 24 is illustrated as including a disc portion 28 having a center post 30 extending vertically therefrom. Inorder to assure substantially equal distribution of the weight 26 over the entire surface 22, the weight 26 is supported on a pin 32 engaged with the center post 30. The disc portion 28 of the head 24 is enclosed within atoroidal head holder 34 which supports a disc shaped pin housing 36 having a central opening which receives both the center post 30 and the pin 32 and maintains them in alignment. Thus, the weight 26 is transmitted through the pin 32 and the center post 30 and is equally distributed over the surface 22 on 'the disc vportion 26 of the head 24. In order to conform the surface 22 tothe curvature of the lapping plate 14, the head 24 can be randomly moved over the lapping plate by randomly moving the transport ring 12 which enclosed the'pin housing 36, head holder'34, and head 24. v

After the head 24 is moved on fthe lapping plate 14 for a suiiiciently long period, the surface 22 thereof will conform to the curvature of the lapping plate 14. The curvature of the lapping plate 14 depends upon three significant factors; namely, the magnitude of weight 26, the thickness of lapping plate 14, and the amount of padding or resilient 4material sandwiched between the' rigid support 18 and the lapping plate 14. By varying the-magnitude of weight 26 and/or the amount of padding llemployed, the desired plate curvature can be established.

FIGURE 3 illustrates an alternative lapping plate ap-y paratus which includes ya base plate 50 having a` wall 52 extending vertically therefrom. Thelapping plate com? prises a flexible diaphragm S4, which can for example be constructed of aluminum, which is secured tothe upper surface of the wall-52 in opposed relationship to the base plate 50. Thus, a subst-antially closed volume is defined between the plates 5) `and 54 and the wall 52. A single opening 56 can be provided to communicate the enclosed volume, through a valve means 58, with means (not shown) for developing either a vacuum or a high pressure within the enclosed volume. If a high pressure is developed, the diaphragm 54 will of course flex upwardly vas illustrated 'by the dotted line 60 so as to develop a concave curvature on the surface of a mechanical member moved thereon.'v On the other hand, if a vacuum is developed in the enclosed volume, the diaphragm 54 will flex tothe position illustrated by dotted line 62 to thereby form la convex surface on the mechanical member moved on the lapping plate 54.

- FIGURE .l illustrates the apparatus for moving the transportk ring 12 over the lapping plate'14 (or 5ft) in a substantially random-like manner while exerting little or no pressurefon the lapping plate. Actually, the apparatus of FIGURE l operates to move the ring 12 in an essentially FIGURE 8 pattern which serves to simulate random motion. The `drive apparatus of FIGURE l includes a motor 70 which through gear box 72 drives pulley 74. V-belti76zengaged with pulley 74 is also frictionally engaged with pulley 7,8 secured to rotatable shaft 8f). Also secured to shaft 80 is a sprocket 82 which is coupled by sprocket chain 84 to a sprocket 86 secured to shaft 88. If the sprockets 82 and 86 have Va 1:2 ratio the ring 12, as should be apparent, permits the. generation of a FGURE 8 pattern. In order to minimize lapping plate Wear, rather than using an exact 1:2 sprocket ratio, a slightly different ratio can .be employed. Thus, a 9:20 sprocket Will generate a Walkingror changing pattern which will prevent rapid plate wear.

Secured to the shaft 80 is a bell crank 90 having an arm 92 .pivoted thereto. The arm 92 is coupled to a pair of members 94 v and 96 which together comprise an A-frame. Members l94 and 96 are secured by swivel bearings l98 and 100 to a plate 162 fixed to the ring 12.

. A bell crank 104 is secured to the shaft 8S.` An arm 106 is coupled by a swivel bearing 108 to the bell crank 104 and by a swivel bearing 11b to the plate 192 fixed to the ring 12.

Inasmuch as the sprocket 82 has approximately half as ymany teeth as the sprocket S6, its rotational speed will be approximately twice as great as that of the sprocket 86. Consequently, the ring 12 will bemoved in a pattern substantially similar to the FIGURE 8 pattern illustrated in FIGURE l. As noted however, the sprocket ratio should preferably be chosen so as to minimize plate WCHI'.

Each of the bell cranks 9) and 164 are provided with longitudinally extending slots therein in which the bearings at the terminals of arms 92 and 06 can be slid-ably adjusted. The effective throw of the cranks can thus be varied by fixing the arm terminals at different points vin the slots. Thus, the heights of the ring movement pattern can be adjusted by varying the position in which the bearing .at the terminal of arm 108 is fixed in the slot of bell crank 191i-, the Aring movement pattern can be adjusted by adjusting the position of the terminal of arm 92 in the slot of bell crank 90.

In the use of the present apparatus, it is desirable to apply the lapping compound Ato a plate which is extremely clean.- Moreover, the lapping compound should be changed reasonably often to` maintain its uniform abrasive characteristics. Movement of the magnetic head 24 in the pattern described, will tend to form circles on the head surface 22 if the weight 26 is distributed evenly on the outer post 30. Any variation of the weight on the post will result in different patterns being formed ondifferent head surfaces utilizing the same lapping apparatus. In order to assure proper distribution of the weight on the post, care should be taken to assure that the pin 32 extends very slightly (c g. .005 inch) above the pin housing 36.

In the actual operation of the apparatus, the head can be initially subjected to a coarse lapping phase during On the other hand, the width of v which a relatively large amount of padding 16 is used uri-der the lapping plate 14 and the magnitude of the Weight 26 is relatively large. The head should be lapped for a certain interval and thereafter should be checked with an optical fiat. In a subsequent finer lapping phase, both the magnitude of the weight and the number of pads used beneath the plate can be reduced and the curvature of the head surface can again be checked with an optical fiat. After a reasonable amount 'of experimentation, an operator will be able to judge with a reasonably high degree of accuracy, exactly what weight, how many pads, and how long each head should be lapped in each phase.

From the foregoing, it should be appreciated that a method and apparatus has been provided herein for re shaping a surface of a mechanical member so as to conform the surface of a desired curvature.

What is claimed is:

1. Apparatus for reshaping a surface on a mechanical member so as to give the surface a precise curvature, said apparatus comprising:

a substantially flat horizontally oriented plate;

said member supported on said plate with said surface in engagement therewith;

means for distorting said plate to said precise curvature; and

means for moving said member in a substantially random manner over said plate.

2. Apparatus for reshaping a surface on a mechanical member so as to give the surface a precise curvature, said apparatus comprising:

a flexible substantially flat horizontally oriented lapping plate having an abrasive surface;

said member supported on said lapping plate with said member surface in engagement with said abrasive surface;

means for distorting said lapping plate to said precise curvature; and

means for moving said member in a substantially random manner over said lapping plate.

3. The apparatus of claim 2 including a base plate having a wall extending upwardly therefrom:

means securing said lapping plate to said wall opposed to said base plate thereby defining a closed volume therebetween; and

wherein said means for distorting said plateincludes means for varying the pressure in said closed volume.

4. The apparatus of claim 2 including a rigid surface and at least one flexible pad supported thereon; and

means supporting said lapping plate on said pad.

5. Apparatus for reshaping a surface on a mechanical member so as to give the surface a precise curvature, said apparatus comprising:

a flexible lapping plate having an abrasive surface;

said member supported on said lapping plate with said member surface in engagement with said abrasive surface;

means for distorting said lapping plate to said precise curvature;

means for moving said member over said plate including first and second bell cranks each rotated at different speeds; a transport ring supported on said abrasive surface enclosing said member; and p first and second arms respectively pivotally secured between said first and second bell cranks and said transport ring.

6. A method of reshaping a surface on a mechanical member so as to give the surface a precise curvature comprising the steps of:

distorting a lapping plate to the curvature desired;

supporting said member on said plate with said surface engaged with said plate; and

moving said member in a substantially random-likefashion on said plate.

7. Apparatus for reshaping a surface On a. magnetic References Cited by the Examiner UNITED STATES PATENTS Gowlland 51-373 X Suverkrop 51-64 Evans 51-373 X Long 51-157 Cloutier 51-154 X Rawstron 51-373 X 10 LESTER M. SWINGLE, Primary Examiner. 

1. APPARATUS FOR RESHAPING A SURFACE ON A MECHANICAL MEMBER SO AS TO GIVE THE SURFACE A PRECISE CURVATURE, SAID APPARATUS COMPRISING: A SUBSTANTIALLY FLAT HORIZONTALLY RIENTED PLATE; SAID MEMBER SUPPORTED ON SAID PLATE WITH SAID SURFACE IN ENGAGEMENT THEREWITH; MEANS FOR DISTORTING SAID PLATE TO SAID PRECISE CURVATURE; AND MEANS FOR MOVING SAID MEMBER IN A SUBSTANTIALLY RANDOM MANNER OVER SAID PLATE. 